Problem 12.5

a) What kind of ions do you expect to predominate with the following analyte/solvent systems in ESI? Complete the table.

Analyte and Solvent

polystyrene in toluene

protein in water/acetonitrile 1:1 + 0.1 % TFA

oligosaccharide in water/methanol 5:1

anionic transition metal complex in chloroform

polycyclic aromatic hydrocarbons in hexane

oligonucleotide in water/isopropanol + amines 50 mM

peptides water/acetonitrile 1:3 + 0.5 % acetic acid

Predominating Ions

…..

…..

…..

…..

…..

…..

…..

b) A synthetic oligonucleotide 8mer has been analyzed by negative-ion ESI mass spectrometry on a linear quadrupole mass spectrometer. The isotopic peaks are not resolved. Determine the molecular weight of the analyte. Follow your intuition.

ESI spectrum of an oligonucleotide. Courtesy of T. Krüger, University of Heidelberg

c) Use the m/z 1184.4 and m/z 789.3 pair of peak to feed the charge deconvolution algorithm. Calculate the molecular weight again.

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